System and method for harmonic control of dual-output generators

ABSTRACT

A dual-output generator is configured to output two or more waveforms at different frequencies. In particular, the dual-output generator is configured to provide low-frequency output, which may be suitable for ultrasonic surgical instruments, and a high-frequency output, which may be suitable for electrosurgical instruments, while reducing the amplitude of all remaining frequencies other than the two selected low and high frequencies to about zero.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/812,736 filed Mar. 9, 2020, which is a continuation of U.S. patentapplication Ser. No. 15/004,923 filed Jan. 23, 2016. The disclosure ofeach of the foregoing applications are hereby incorporated by referencein its entirety herein.

BACKGROUND Technical Field

The present disclosure relates to systems and methods for simultaneouslypowering surgical energy devices at multiple frequencies. In particular,the present disclosure relates to a generator configured tosimultaneously power one or more outputs at specified frequencies andregulated amplitude suitable for powering a first device at a firstfrequency and a second device at a second frequency, which is differentfrom the first frequency.

Background of Related Art

Electrosurgery involves application of high radio frequency (“RF”)electrical current to a surgical site to cut, ablate, desiccate, orcoagulate tissue. In monopolar electrosurgery, a source or activeelectrode delivers radio frequency alternating current from the RFgenerator to the targeted tissue. A patient return electrode is placedremotely from the active electrode to conduct the current back to thegenerator.

In bipolar electrosurgery, return and active electrodes are placed inclose proximity to each other such that an electrical circuit is formedbetween the two electrodes (e.g., in the case of an electrosurgicalforceps). In this manner, the applied electrical current is limited tothe body tissue positioned between the electrodes. Accordingly, bipolarelectrosurgery generally involves the use of instruments where it isdesired to achieve a focused delivery of electrosurgical energy betweentwo electrodes positioned on the instrument, e.g. forceps or the like.

Ultrasonic surgical devices have also been demonstrated to providehemostasis and efficient dissection of tissue with minimum lateralthermal damage and low smoke generation. Unlike electrosurgical devices,which require electrical current to flow through a patient, ultrasonicsurgical devices operate by applying mechanical motion through anultrasonic probe using an ultrasonic transducer that is driven at aresonant frequency.

Each of the electrosurgical and ultrasonic devices has their desireduses due to their inherent operational characteristics. Accordingly,there is a need for a system and a generator configured to operate bothtypes of the instruments simultaneously to provide for new and improvedsurgical techniques and applications.

SUMMARY

The present disclosure provides a dual-output generator configured tooutput two or more waveforms at different frequencies allowing thedual-output generator to provide low-frequency output, which may besuitable for ultrasonic surgical instruments, and a high-frequencyoutput, which may be suitable for electrosurgical instruments, whilereducing the amplitude of all remaining frequencies other than the twoselected low and high frequencies to about zero.

According to an embodiment of the present disclosure, a dual-outputelectrosurgical generator is provided. The generator includes a powersupply configured to output a DC waveform and an inverter coupled to thepower supply. The inverter includes at least one switching elementoperated at a switching angle. The generator also includes a controllercoupled to the inverter and configured to modulate the switching angleto generate a first waveform at a first frequency and a secondarywaveform at a second frequency.

According to another embodiment of the present disclosure, anelectrosurgical system is provided. The system includes a dual-outputelectrosurgical generator having a power supply configured to output aDC waveform and an inverter coupled to the power supply. The inverterincludes at least one switching element operated at a switching angle.The generator also includes a controller coupled to the inverter andconfigured to modulate the switching angle to generate a first waveformat a first frequency and a secondary waveform at a second frequency. Thegenerator further includes a first output outputting the first waveformand a second output outputting the second waveform. The system alsoincludes a first instrument coupled to the first output and energizableby the first waveform and a second instrument coupled to the secondoutput and energizable by the second waveform.

According to an aspect of the above-described embodiment, the firstinstrument is an ultrasonic instrument including a transducerenergizable by the first waveform and the second instrument is anelectrosurgical instrument including at least one electrode configuredto contact tissue and transmit the second waveform thereto.

According to one aspect of the above-described embodiment, the firstinstrument is a first electrosurgical instrument including at least onefirst electrode configured to contact tissue and transmit the firstwaveform thereto and the second instrument is a second electrosurgicalinstrument including at least second one electrode configured to contacttissue and transmit the second waveform thereto.

According to an aspect of any of the above-described embodiments, thefirst frequency is a fundamental frequency, the second frequency is aharmonic frequency of the fundamental frequency, and the secondfrequency is higher than the first frequency.

According to another aspect of any of the above-described embodiments,the generator further includes a low-frequency filter coupled to theinverter and configured to output the first waveform and ahigh-frequency filter coupled to the inverter and configured to outputthe second waveform.

According to a further aspect of any of the above-described embodiments,the inverter includes four switching elements arranged in an H-bridgetopology and each of the switching elements may be a wide bandgap fieldeffect transistor.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be understood by reference to theaccompanying drawings, when considered in conjunction with thesubsequent, detailed description, in which:

FIG. 1 is a perspective view of a surgical system according to anembodiment of the present disclosure;

FIG. 2 is a front view of a dual-output generator of FIG. 1 according toan embodiment of the present disclosure;

FIG. 3 is a schematic diagram of the dual-output generator of FIG. 2according to an embodiment of the present disclosure;

FIG. 4 is an electrical schematic diagram of the dual-output generatorof FIG. 2 according to an embodiment of the present disclosure;

FIG. 5 is a schematic diagram of another embodiment of a DC-AC inverterof the dual-output generator of FIG. 1;

FIG. 6 is a plot of a unipolar switching angle waveform for generating asinusoidal low frequency waveform and a high frequency waveformaccording to an embodiment of the present disclosure;

FIG. 7 is a plot of a bipolar switching angle waveform for generating asinusoidal low frequency waveform and a high frequency waveformaccording to an embodiment of the present disclosure;

FIG. 8 is a bar graph of harmonic frequencies of the waveforms generatedby the unipolar switching angle waveform of FIG. 6; and

FIG. 9 is a bar graph of harmonic frequencies of the waveforms generatedby the bipolar switching angle waveform of FIG. 7.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure will be described belowwith reference to the accompanying drawings. In the followingdescription, well-known functions or constructions are not described indetail to avoid obscuring the present disclosure in unnecessary detail.Those skilled in the art will understand that the present disclosure maybe adapted for use with either an endoscopic instrument, a laparoscopicinstrument, or an open instrument. It should also be appreciated thatdifferent electrical and mechanical connections and other considerationsmay apply to each particular type of instrument.

A generator according to the present disclosure can operate ultrasonicand electrosurgical instruments at multiple frequencies. In particular,the generator may be used in monopolar and/or bipolar electrosurgicalprocedures, including, for example, cutting, coagulation, ablation, andvessel sealing procedures. The generator may include a plurality ofoutputs for interfacing with various ultrasonic and electrosurgicalinstruments (e.g., ultrasonic dissectors and hemostats, monopolarinstruments, return electrode pads, bipolar electrosurgical forceps,footswitches, etc.). Further, the generator includes electroniccircuitry configured to generate radio frequency energy specificallysuited for powering ultrasonic instruments and electrosurgical devicesoperating in various electrosurgical modes (e.g., cut, blend, coagulate,division with hemostasis, fulgurate, spray, etc.) and procedures (e.g.,monopolar, bipolar, vessel sealing).

FIG. 1 is a perspective view of the components of one illustrativeembodiment of a dual-output system 10 according to the presentdisclosure. The system 10 may include one or more monopolarelectrosurgical instruments 20 having one or more active electrodes 23(e.g., electrosurgical cutting probe, ablation electrode(s), etc.) fortreating tissue of a patient. Electrosurgical alternating RF current issupplied to the instrument 20 by a generator 200 via a supply line 24that is connected to an active terminal 230 (FIG. 3) of the generator200, allowing the instrument 20 to cut, coagulate, thermally ornon-thermally ablate and/or otherwise treat tissue. The alternatingcurrent is returned to the generator 200 through a return electrode pad26 via a return line 28 at a return terminal 232 (FIG. 3) of thegenerator 200. For monopolar operation, the system 10 may include aplurality of return electrode pads 26 that, in use, are disposed on apatient to minimize the chances of tissue damage by maximizing theoverall contact area with the patient. In addition, the generator 200and the return electrode pads 26 may be configured for monitoringtissue-to-patient contact to ensure that sufficient contact existstherebetween.

The system 10 may also include one or more bipolar electrosurgicalinstruments, for example, a bipolar electrosurgical forceps 30 havingone or more electrodes for treating tissue of a patient. Theelectrosurgical forceps 30 includes a housing 31 and opposing jawmembers 33 and 35 disposed at a distal end of a shaft 32. The jawmembers 33 and 35 have one or more active electrodes 34 and a returnelectrode 36 disposed therein, respectively. The active electrode 34 andthe return electrode 36 are connected to the generator 200 through cable38 that includes the supply and return lines 24, 28, which may becoupled to the active and return terminals 230, 232, respectively (FIG.3). The electrosurgical forceps 30 is coupled to the generator 200 at aport having connections to the active and return terminals 230 and 232(e.g., pins) via a plug disposed at the end of the cable 38, wherein theplug includes contacts from the supply and return lines 24, 28 asdescribed in more detail below.

The system 10 also includes an ultrasonic surgical instrument 40, whichincludes a housing 42 having an ultrasonic transducer 44 disposedtherein. The ultrasonic surgical instrument 40 also includes anelongated shaft 46 having an end effector 48 disposed at a distal endthereof. The distal end effector 48 includes a movable jaw member 50 anda probe 52. The ultrasonic transducer 44 is connected to the generator200 via a cable 54 that includes supply lines 56 and 58 coupled toactive and return terminals 234 and 236 (FIG. 3), respectively. Theultrasonic probe 52 is coupled to the ultrasonic transducer 44, suchthat when the ultrasonic transducer 44 is actuated in response to RFcurrent from the generator 200, the ultrasonic transducer 44 generatesultrasonic mechanical motion within the probe 52, which may be used toseal and/or cut tissue.

With reference to FIG. 2, a front face 240 of the generator 200 isshown. The generator 200 may include a plurality of ports 250-262 toaccommodate various types of electrosurgical instruments (e.g.,monopolar electrosurgical instrument 20, electrosurgical forceps 30,ultrasonic surgical instrument 40, etc.).

The generator 200 includes a user interface 241 having one or moredisplay screens 242, 244, 246 for providing the user with variety ofoutput information (e.g., intensity settings, treatment completeindicators, etc.). Each of the screens 242, 244, 246 is associated witha corresponding port 250-262. The generator 200 includes suitable inputcontrols (e.g., buttons, activators, switches, touch screen, etc.) forcontrolling the generator 200. The screens 242, 244, 246 are alsoconfigured as touch screens that display a corresponding menu for theinstruments (e.g., electrosurgical forceps 30, etc.). The user thenadjusts inputs by simply touching corresponding menu options.

Screen 242 controls monopolar output and the devices connected to theports 250 and 252. Port 250 is configured to couple to a monopolarelectrosurgical instrument (e.g., electrosurgical instrument 20) andport 252 is configured to couple to a foot switch (not shown). The footswitch provides for additional inputs (e.g., replicating inputs of thegenerator 200). Screen 244 controls monopolar and bipolar output and thedevices connected to the ports 256 and 258. Port 256 is configured tocouple to other monopolar instruments. Port 258 is configured to coupleto a bipolar instrument (not shown).

Screen 246 controls the electrosurgical forceps 30 and the ultrasonicsurgical instrument 40 that may be plugged into the ports 260 and 262,respectively. The generator 200 outputs energy through the port 260suitable for sealing tissue grasped by the electrosurgical forceps 30.In particular, screen 246 outputs a user interface that allows the userto input a user-defined intensity setting for each of the ports 260 and262. The user-defined setting may be any setting that allows the user toadjust one or more energy delivery parameters, such as power, current,voltage, energy, etc. or sealing parameters, such as energy ratelimiters, sealing duration, etc. The user-defined setting is transmittedto the controller 224 where the setting may be saved in memory 226. Inembodiments, the intensity setting may be a number scale, such as forexample, from one to ten or one to five. In embodiments, the intensitysetting may be associated with an output curve of the generator 200. Theintensity settings may be specific for each electrosurgical forceps 30being utilized, such that various instruments provide the user with aspecific intensity scale corresponding to the electrosurgical forceps30.

The active and return terminals 230 and 232 and the active and returnterminals 234 and 236 may be coupled to any of the desired ports250-262. In embodiments, the active and return terminals 230 and 232 maybe coupled to the ports 250-260 and the active and return terminals 234and 236 may be coupled to the port 262.

FIG. 3 shows a schematic block diagram of the generator 200 configuredto output low-frequency waveform for energizing a first instrument andhigh-frequency waveform for energizing a second instrument. Inparticular, FIG. 3 shows the generator 200 is outputting low-frequencywaveform to the transducer 44 (FIG. 1) of the ultrasonic surgicalinstrument 40 and a high-frequency waveform to the monopolarelectrosurgical instrument 20 and/or electrosurgical forceps 30. Thegenerator 200 is also configured to output low-frequency energy forenergizing any suitable electrosurgical instrument and outputhigh-frequency energy for energizing another electrosurgical instrument.In embodiments, the electrosurgical instruments may be the same (e.g.,monopolar electrosurgical instrument 20) such that each of the twoelectrosurgical instruments is operated at a separate frequency. Infurther embodiments, the electrosurgical instruments may be different,such that one of the instruments (e.g., monopolar electrosurgicalinstrument 20) is operated at a low-frequency and another instrument(e.g., electrosurgical forceps 30) is operated at a high-frequency.

The generator 200 includes a controller 224, a power supply 227, and adual frequency inverter 228. The power supply 227 may be a high voltage,DC power supply connected to an AC source (e.g., line voltage) andprovides high voltage, DC power to the dual-frequency inverter 228,which then converts high voltage, DC power into treatment energy (e.g.,electrosurgical or ultrasonic) and delivers the energy to the activeterminals 230 and 234. The energy is returned thereto via the returnterminals 232 and 236. In particular, electrical energy for theultrasonic instrument 40 is delivered through the active and returnterminals 234 and 236 and electrosurgical energy for energizing themonopolar electrosurgical instrument 20 and/or electrosurgical forceps30 is delivered through the active and return terminals 230 and 232. Theactive terminals 230, 234 and return terminals 232, 236 are coupled tothe dual-frequency inverter 228 through an isolation transformer 229.

The isolation transformer 229 includes a primary winding 229 a coupledto the dual-frequency inverter 228, a first secondary winding 229 bcoupled to a low pass filter 304, and a second secondary winding 229 ccoupled to a high pass filter 306. The low pass filter 304 is configuredto pass through only the low-frequency current generated by thedual-frequency inverter 228, which is then supplied to the active andreturn terminals 234 and 236. The high pass filter 306 is configured topass through only the high frequency current generated by thedual-frequency inverter 228, which is then supplied to the active andreturn terminals 230 and 232. In embodiments, the low pass filter 304and the high pass filter 306 may be inductor/capacitor filters, whichare tuned at their respective resonant frequencies.

The dual-frequency inverter 228 is configured to operate in a pluralityof modes, during which the generator 200 outputs corresponding waveformshaving specific duty cycles, peak voltages, crest factors, etc. It isenvisioned that in other embodiments, the generator 200 may be based onother types of suitable power supply topologies. Dual-frequency inverter228 may be a resonant RF amplifier or a non-resonant RF amplifier. Anon-resonant RF amplifier, as used herein, denotes an amplifier lackingany tuning components, i.e., conductors, capacitors, etc., disposedbetween the RF inverter and the filters 304 and 306.

The controller 224 includes a processor (not shown) operably connectedto a memory (not shown), which may include one or more of volatile,non-volatile, magnetic, optical, or electrical media, such as read-onlymemory (ROM), random access memory (RAM), electrically-erasableprogrammable ROM (EEPROM), non-volatile RAM (NVRAM), or flash memory.The processor may be any suitable processor (e.g., control circuit)adapted to perform the operations, calculations, and/or set ofinstructions described in the present disclosure including, but notlimited to, a hardware processor, a field programmable gate array(FPGA), a digital signal processor (DSP), a central processing unit(CPU), a microprocessor, and combinations thereof. Those skilled in theart will appreciate that the processor may be substituted for by usingany logic processor (e.g., control circuit) adapted to perform thecalculations and/or set of instructions described herein.

The controller 224 includes an output port that is operably connected tothe power supply 227 and/or dual-frequency inverter 228 allowing theprocessor to control the output of the generator 200 according to eitheropen and/or closed control loop schemes. A closed loop control scheme isa feedback control loop, in which a plurality of sensors measure avariety of tissue and energy properties (e.g., tissue impedance, tissuetemperature, output power, current and/or voltage, etc.), and providefeedback to the controller 224. The controller 224 then controls thepower supply 227 and/or dual-frequency inverter 228, which adjusts theDC and/or power supply, respectively, including, but not limited to,field programmable gate array, digital signal processor, andcombinations thereof.

The generator 200 according to the present disclosure may also include aplurality of sensors (not shown). The sensors may be coupled to powersupply 227 and/or dual-frequency inverter 228 and may be configured tosense properties of DC current supplied to the dual-frequency inverter228 and/or RF energy outputted by the dual-frequency inverter 228,respectively. Various components of the generator 200, namely, thedual-frequency inverter 228, the current and voltage sensors, may bedisposed on a printed circuit board (PCB). The controller 224 alsoreceives input signals from the input controls of the generator 200, theinstrument 20 and/or electrosurgical forceps 30. The controller 224utilizes the input signals to adjust power outputted by the generator200 and/or performs other control functions thereon.

With reference to the schematic shown in FIG. 4, the generator 200includes a DC-DC buck converter 301 and the dual-frequency inverter 228.In the exemplary embodiment, the power supply 227 may be connected toDC-DC buck converter 301. Furthermore, an inductor 303 is electricallycoupled between DC-DC buck converter 301 and dual-frequency inverter228. The output of dual-frequency inverter 228 transmits power to theprimary winding 229 a of transformer 229, which passes through thesecondary winding of transformer 229 to the load, e.g., tissue beingtreated, the ultrasonic transducer 44, etc.

DC-DC buck converter 301 includes a switching element 301 a anddual-frequency inverter 228 includes a plurality of switching elements302 a-302 d arranged in an H-bridge topology. In embodiments,dual-frequency inverter 228 may be configured according to any suitabletopology including, but not limited to, half-bridge, full-bridge,push-pull, and the like. Suitable switching elements includevoltage-controlled devices such as transistors, field-effect transistors(FETs), combinations thereof, and the like. In embodiments, the FETs maybe formed from gallium nitride, aluminum nitride, boron nitride,silicone carbide, or any other suitable wide bandgap material.

FIG. 5 shows another embodiment of the generator 200, which differs fromthe embodiment of FIGS. 3 and 4 in that the low pass filter 304 and highpass filter 306 are coupled directly to the dual-frequency inverter 228rather than the first secondary winding 229 b and the second secondarywinding 229 c of the isolation transformer 229, respectively. Each ofthe low pass filter 304 and the high pass filter 306 includes anisolation transformer 308 and 310, respectively. The low pass filter 304is coupled to a primary winding 308 a of the isolation transformer 308and high pass filter 306 is coupled to a primary winding 310 a of theisolation transformer 310. The active terminal 234 and return terminal236 are coupled to a secondary winding 308 b of the isolationtransformer 308 and the active terminal 230 and the return terminal 232are coupled to a secondary winding 310 b of the isolation transformer310.

The controller 224 is in communication with both DC-DC buck converter301 and dual-frequency inverter 228, in particular, the switchingelements 301 a and 302 a-302 d, respectively. Controller 224 isconfigured to output control signals, which may be a pulse-widthmodulated signal, to switching elements 301 a and 302 a-302 d asdescribed in further detail in co-pending application published as US2014/0254221, entitled CONSTANT POWER INVERTER WITH CREST FACTORCONTROL, filed on Dec. 4, 2013 by Johnson et al., the entire contents ofwhich are incorporated by reference herein. In particular, controller224 is configured to modulate a control signal d₁ supplied to switchingelement 301 a of DC-DC buck converter 301 and control signals d₂supplied to switching elements 302 a-302 d of dual-frequency inverter228. Additionally, controller 224 is configured to measure powercharacteristics of generator 200, and control generator 200 based atleast in part on the measured power characteristics. Examples of themeasured power characteristics include the current through inductor 103and the voltage at the output of dual-frequency inverter 228. In anexemplary embodiment, controller 224 controls buck converter 301 bygenerating the control signal d₁ based on a comparison of the inductorcurrent and a nonlinear carrier control current for every RF cycle.

The generator 200 according to the present disclosure, and inparticular, the controller 224 is configured to operate thedual-frequency inverter 228 using a dual-frequency selective harmonicelimination (“DFSHE”) modulation method. Moreover, the DFSHE modulationaccording to the present disclosure is applicable to a variety of DC/ACtopologies, such as half-bridge, full bridge, multilevel inverter, andresonant type inverters and the dual-frequency inverter 228 is anexemplary embodiment. In DFSHE modulation, the controller 200 signalsthe dual-frequency inverter 228 to generate two individual frequencies,while diminishing undesired harmonics. The controller 224 is configuredto generate a pulse-width modulated control signals to the switchingelements 302 a-302 d. Each of the control signals is based on switchingangles for each of the switching elements 302 a-302 d, which whenactivated generate a low-frequency waveform for energizing thetransducer 44 or any other suitable instrument, such as the monopolarelectrosurgical instrument 20 or the electrosurgical forceps 30. Thelow-frequency waveform may have a fundamental frequency from about 10kHz to about 100 kHz, in embodiments, from about 30 kHz to about 70 kHz.The low-frequency waveform also generates a plurality of harmonicwaveform. Since not all of the resulting waveforms are suitable, onlyone of the higher harmonic waveforms may be used in addition to thefundamental waveform. In particular, a kth harmonic waveform, which is ahigh frequency waveform, may be used for energizing one of theelectrosurgical instruments, such as, the monopolar electrosurgicalinstrument 20 or the electrosurgical forceps 30. Thus, the switchingangles for activating the switching elements 302 a-302 d are selectedthat generate the low-frequency waveform and a high frequency waveform,which is a kth harmonic of the low-frequency waveform.

With reference to FIGS. 6 and 7, exemplary switching angle waveforms forgenerating dual-frequency outputs are shown. FIG. 6 shows a quartersymmetric, unipolar switching angle waveform 600 for generating asinusoidal low frequency waveform 602 and a sinusoidal high frequencywaveform 604. The unipolar switching angle waveform 600 includes aplurality of pulses 600 a, b, c, . . . n corresponding to the switchingangles for each of the switching elements 302 a-302 d (FIGS. 4 and 5).The pulses of the switching angle waveform 600 also correspond to thepositive and negative cycles of each of the low frequency waveform 602and a high frequency waveform 604.

All of the positive and negative cycles of the unipolar switching anglewaveform 600 produce the positive and negative cycles of the lowfrequency waveform 602. In particular, there are multiple switchingpulses 600 a, b, c, . . . n of varying duration per period of the lowfrequency waveform 602 and the high frequency waveform 604. The term“period” as used herein denotes the time it takes to complete one fullcycle of a waveform. Thus, for each period of the low frequency waveform602, there are ten (10) switching pulses 600 a, b, c, . . . n, five (5)per half cycle/period and the switching pulses 600 a, b, c, . . . n areof different duration. Similarly, for each period of the high frequencywaveform 604 there is at least one complete and one partial switchingpulse of different duration as illustrated in FIG. 6. Each of the pulses600 a, b, c, . . . n be calculated by the controller 224 based on adesired frequencies of the low frequency waveform 602 and the highfrequency waveform 604.

FIG. 7 shows a quarter symmetric bipolar switching angle waveform 700for generating a sinusoidal low frequency waveform 702 and a sinusoidalhigh frequency waveform 704. The bipolar switching angle waveform 700includes a plurality of pulses 700 a, b, c, . . . n corresponding to theswitching angles for each of the switching elements 302 a-302 d. Thepulses of the switching angle waveform 700 also correspond to thepositive and negative cycles of each of the low frequency waveform 702and a high frequency waveform 704.

All of the positive and negative cycles of the bipolar switching anglewaveform 700 produce the positive and negative cycles of the lowfrequency waveform 702. In particular, there are multiple switchingpulses 700 a, b, c, . . . n of varying duration per period of the lowfrequency waveform 702 and the high frequency waveform 704. Thus, foreach period of the low frequency waveform 702, there are ten (10)switching pulses 700 a, b, c, . . . n, five (5) per half cycle/periodand the switching pulses 700 a, b, c, . . . n are of different duration.Similarly, for each period of the high frequency waveform 704 there isat least one complete and one partial switching pulse of differentduration as illustrated in FIG. 7. The pulses 700 a, b, c, . . . n areof varying duration and may be calculated by the controller 224 based ona desired frequencies of the low frequency waveform 702 and the highfrequency waveform 704.

Frequencies of each of the low frequency waveforms 602, 702 and the highfrequency waveforms 604, 704 may be set by a user using the userinterface 241. The controller 224 may then calculate the switchingangles for generating the waveforms 602, 604, 702, and 704. Inparticular, the controller 224 may calculate the number, frequency, andduration of the switching angles, e.g., duration of the pulses 600 a, b,c, . . . n and 700 a, b, c, . . . n. In embodiments, these propertiesmay be calculated offline either by the controller 224 or any othersuitable processor.

FIGS. 8 and 9 show harmonic frequency plots 800 and 900 generated by theswitching angle waveforms 600 and 700, respectively. The plots 800 and900 are bar graphs illustrating the frequency content of the waveforms600 and 700, respectively, number of harmonics and their amplitude. Thefundamental frequency waveform is shown as the first bar in each of theplots 800 and 900 and is the low frequency waveform 602 and 702. Thehigh frequency waveforms 604 and 705 are higher kth harmonic waveforms.The plots 800 and 900 also show that the DFSHE modulation method alsoeliminates all of the harmonic waveforms between the low frequencywaveforms 602, 702 and high frequency waveforms 604, 704.

To decouple and control the amplitude of simultaneous waveforms 602, 604and 702, 704, the present disclosure utilizes a DFSHE modulation method,which allows for fundamental and certain harmonics to be independentlycontrolled. This also allows for individual power regulation andelimination of undesired harmonics, which reduces energy losses andelectro-magnetic interference. The pulses 600 a, b, c, . . . n of thequarter symmetric unipolar waveform 600 are calculated using DFSHEalgorithm according to the present disclosure. Fourier expansion of thisswitching angle waveforms 600 or 700 may be done using the formula (1)below:

$\begin{matrix}{{v\left( {\omega\; t} \right)} = {\sum\limits_{{n = 1},3,5,\ldots}^{\infty}\;{{\frac{4V_{dc}}{n\;\pi}\left\lbrack {{\cos\left( {n\;\theta_{1}} \right)} - {\cos\left( {n\;\theta_{2}} \right)} + {\cos\left( {n\;\theta_{3}} \right)} - \ldots + {\cos\left( {n\;\theta_{m}} \right)}} \right\rbrack} \cdot {\sin\left( {n\;\omega\; t} \right)}}}} & (1)\end{matrix}$

Since the two components, namely, the waveforms 602 and 604 or thewaveforms 702 or 704, to be synthesized are a low-frequency element andits kth harmonic. Under these conditions, the Fourier expansion of (1)is rearranged to form a system of equations as illustrated in formula(2) below:

$\begin{matrix}\left\{ \begin{matrix}{{{\frac{4V_{dc}}{\pi}\left( {{\cos\mspace{14mu}\theta_{1}} - {\cos\mspace{14mu}\theta_{2}\cdots} + {\cos\mspace{14mu}\theta_{m}}} \right)} = V_{LF}}\mspace{40mu}} \\{{{{\cos\mspace{14mu} 3\theta_{1}} - {\cos\mspace{14mu} 3\theta_{2}\cdots} + {\cos\mspace{14mu} 3\theta_{m}}} = 0}\mspace{104mu}} \\{{{{\cos\mspace{14mu} 5\theta_{1}} - {\cos\mspace{14mu} 5\theta_{2}\cdots} + {\cos\mspace{14mu} 5\theta_{m}}} = 0}\mspace{104mu}} \\{{\frac{4V_{dc}}{\pi}\left( {{\cos\mspace{14mu} k\;\theta_{1}} - {\cos\mspace{14mu} k\;\theta_{2}\cdots} + {\cos\mspace{14mu} k\;\theta_{m}}} \right)} = V_{HF}} \\{{\ldots\ldots}\mspace{430mu}} \\{{{{\cos\mspace{14mu} n\;\theta_{1}} - {\cos\mspace{14mu} n\;\theta_{2}\cdots} + {\cos\mspace{14mu} n\;\theta_{m}}} = 0}\mspace{104mu}}\end{matrix} \right. & (2)\end{matrix}$

Solving formula (2) generates the switching angles, namely, pulses 600a, b, c, . . . n or pulses 700 a, b, c, . . . n, for synthesizing thedesired dual-frequency output. In embodiments, two solver loops may beemployed to solve the transcendental equations of formula (2).

In traditional PWM modulation schemes, only fundamental frequencywaveform is generated and controlled, while unregulated harmonics arefiltered. In the DFSHE modulation according to the present disclosure,however, both fundamental frequency waveform, e.g., low frequencywaveform 602 or 702, and the kth harmonic waveforms, e.g., highfrequency waveforms 604 and 704, are simultaneously generated andaccurately modulated, and undesired harmonics, namely, frequenciesbetween, below, and/or near the desired frequencies are eliminated. Asillustrated in FIGS. 8 and 9, the DFSHE modulation according to thepresent disclosure, allows for regulation of the waveform amplitude atall frequencies between the low and high controlled frequencies to zero.In addition, harmonics above the selected highest controlled frequencymay also be eliminated.

Moreover, unlike harmonic utilization techniques, the fundamental andthe kth harmonic waveforms are decoupled in modulation, which providesfor individual power regulation of these waveforms. These features ofDFSHE modulation according to the present disclosure make itparticularly useful in electrosurgical generators, which previouslyrelied on dual-inverter configurations to achieve dual-frequency output.Compared with multilevel inverters or dual-inverter configurations,another advantages of the generators, systems, and method according tothe present disclosure is that no additional switching devices arerequired, which significantly reduces overall costs while achievingequivalent regulation performance.

While several embodiments of the disclosure have been shown in thedrawings and/or described herein, it is not intended that the disclosurebe limited thereto, as it is intended that the disclosure be as broad inscope as the art will allow and that the specification be read likewise.Therefore, the above description should not be construed as limiting,but merely as exemplifications of particular embodiments. Those skilledin the art will envision other modifications within the scope and spiritof the claims appended hereto.

1-19. (canceled)
 20. A dual frequency inverter comprising: at least oneswitching element operated at a switching angle; and a controllercoupled to the at least one switching element and configured to modulatethe switching angle using dual-frequency selective harmonic eliminationmodulation to simultaneously generate a first waveform at a firstfrequency and a secondary waveform at a second frequency and eliminateat least one harmonic waveform between the first frequency and thesecond frequency.
 21. The dual frequency inverter according to claim 20,wherein the first frequency is a fundamental frequency.
 22. The dualfrequency inverter according to claim 21, wherein the second frequencyis a harmonic frequency of the fundamental frequency.
 23. The dualfrequency inverter according to claim 20, further comprising: alow-frequency filter configured to output the first waveform.
 24. Thedual frequency inverter according to claim 20, further comprising: ahigh-frequency filter configured to output the second waveform.
 25. Thedual frequency inverter according to claim 20, wherein the at least oneswitching element includes four switching elements arranged in anH-bridge topology.
 26. The dual frequency inverter according to claim25, wherein each of the switching elements is a wide bandgap fieldeffect transistor.
 27. The dual frequency inverter according to claim20, wherein the second frequency is higher than the first frequency. 28.A dual-output electrosurgical generator comprising: a dual frequencyinverter including at least one switching element operated at aswitching angle; a controller coupled to the dual frequency inverter andconfigured to modulate the switching angle using dual-frequencyselective harmonic elimination modulation to simultaneously to generatea first waveform at a first frequency and a secondary waveform at asecond frequency and eliminate at least one harmonic waveform betweenthe first frequency and the second frequency; a first output outputtingthe first waveform; and a second output outputting the second waveform.29. The dual-output electrosurgical generator according to claim 28,wherein the first frequency is a fundamental frequency.
 30. Thedual-output electrosurgical generator according to claim 29, wherein thesecond frequency is a harmonic frequency of the fundamental frequency.31. The dual-output electrosurgical generator according to claim 28,wherein the dual frequency inverter further includes a low-frequencyfilter coupled to the dual frequency inverter and configured to outputthe first waveform.
 32. The dual-output electrosurgical generatoraccording to claim 28, wherein the dual frequency inverter furtherincludes a high-frequency filter coupled to the dual frequency inverterand configured to output the second waveform.
 33. The dual-outputelectrosurgical generator according to claim 28, wherein the at leastone switching element includes four switching elements arranged in anH-bridge topology.
 34. The dual-output electrosurgical generatoraccording to claim 33, wherein each of the switching elements is a widebandgap field effect transistor.
 35. The dual-output electrosurgicalgenerator according to claim 28, wherein the second frequency is higherthan the first frequency.